This invention relates to an intraocular lens designed to be inserted in a capsular sac in an eye.
Intraocular lenses are designed to correct aphakia during an operation for a cataract. A cataract is characterized by the progressive loss of vision because the cornea in the patient""s eye becomes opaque. A surgical operation is performed to extract the opacified cornea and to replace it with an artificial cornea called an intraocular lens. The intraocular lens may be placed in the anterior chamber in front of the iris or in the posterior chamber behind the iris, in a ciliary seat or in the capsular sac of the eye. The lens is composed of two parts, an optical part enabling vision that may be single-focal or multi-focal, and a support or haptic portion that will interact with the tissues by mechanical thrust and cellular growth and hold the lens in position in the eye. There are two types of implants used to replace the natural cornea at the present time, namely xe2x80x9crigidxe2x80x9d implants and xe2x80x9cflexiblexe2x80x9d implants.
Polymethylmethacrylate (PMMA) is usually used for rigid intraocular lenses. The flexible implant can bend and be inserted through a very small cornean or scleral incision about 3 millimeters long, after extraction of the natural lens nucleus from the capsular sac. This technique reduces residual astigmatism. Many intraocular lenses made of flexible material have already been proposed. For example, these lenses may be made from polysiloxanes, or flexible hydrophobic or hydrophilic acrylic polymers (copolyhema). Intraocular lenses made of co-polyhema are made by machining in the dry state, and the material will then be hydrated to make it flexible.
A flexible single piece intraocular lens disclosed in French Patent Application FR 2 766 699, is designed to prevent movement of the lens optics along the optical axis when the lens is being put into place. This lens is shown in FIG. 4. In order to achieve this purpose, closed haptic portions 410 having legs 411, 412 that are not radial are used. Thus, in theory, forces transmitted through the legs 411, 412 onto the optical part 401 when the lens is in position in the capsular sac of the eye do not have a radial component. Consequently, the optical part 401 should not move or be deformed. However, note that according to FIG. 4, the longitudinal axes of the legs 411, 412 for each haptic portion 410 intersect at a point Sxe2x80x2 that is in the angular section with center O and with an arc defined by the contact portion 414 of the haptic portion joining the free ends of the legs 411, 412. Once the lens is in position, centripetal forces will be applied to each haptic portion 410. Considering the geometry of each haptic portion defined above, these forces will induce a rotation moment on each leg 411, 412. According to FIG. 4, these two rotation moments will have opposite signs. If the values of these two moments are the same, then the haptic portion will simply be compressed, which will necessarily cause buckling of legs. If the sum of the moments is not zero, the leg with the smallest moment will be compressed and the haptic portion will pivot towards the direction of the highest moment. Thus, in all cases, at least one leg will be compressed. This compression phenomenon is also illustrated in FIG. 5a in which the shape of a hapic portion as illustrated in FIG. 4 is shown. In this figure, the compression C exerted on the haptic portion when the lens is in position causes a centripetal component Fc1 and a tangential component Ft1 to be applied to each leg 411, 412. Due to the particular geometry of the haptic portion of the lens, the signs of these tangential components Ft1 are opposite and are in opposite directions. Depending on the value of these forces, the phenomena described above will be applied to each leg 411, 412. These phenomena will generate an accumulation of stresses that will result either in random deformation of the leg(s) causing instability in the position of the optical part, or an additional pressure exerted on the peripheral tissues of the capsular sac that can cause complications for the patient. These phenomena may also occur when the geometry of each haptic portion is such that the two legs are facing inwards instead of outwards as shown in FIG. 5b. In this case, the tangential components Ft2 will be towards each other.
The purpose of this invention is to overcome the disadvantages of prior art by proposing an intraocular lens in which the haptic portions do not cause any displacement of the optical part along the optical axis, or stress accumulation on the optical part or on the peripheral tissues.
This objective is achieved by an intraocular lens comprising an optical part approximately in the shape of a disk and a support part or haptic portion comprising two closed pairs of haptic portions laid out symmetrically about a first diameter of the optical part, the haptic portions in each pair being symmetrical with each other about a second diameter approximately perpendicular to the first diameter, characterized in that each haptic portion is provided with two arms or side segments in which a first end is fixed to the periphery of the optical part and, for each haptic portion, the longitudinal axes of the side segments intersect at a point that is not included in an angular sector with the same center as the optical center of the optical part, and in which the arc consists of a contact portion joining the second ends of the side segments of the same haptic portion.